"The bulk cash distribution site was used by [Isis] to distribute money to fund terrorist activities," Lieutenant Commander Ben Tisdale, a US spokesman, was quoted as saying by The Guardian.

"We estimate (the storage had) millions of dollars from all their illicit stuff: oil, looting, extortion," AFP quoted an official as saying.

Two 900-kg bombs targeted the building at dawn on Monday to minimise civilian casualty. During the day, civilians were found around the structure and at night Isis personnel. The timing of the strike was thus reportedly set up to kill as few civilians as possible. However, five to seven civilian deaths have been reported.

The coalition members were prepared for up to 50 civilian deaths as this would have been a significant target, which is part of the new policy the Pentagon has taken towards attacking the Islamic militant group.

The Pentagon had, in a previous statement, said it was ready to amp up attacks even if it put more civilians in the line of fire, provided the targets were significant for dismantling the jihadi outfit.

The anti-Isis coalition has also been increasingly targeting the money-minting ability of Isis that would affect its ability to function like a state, reported CNN.

Isis oil trucks bound out of Syria have also become targets of airstrikes.

However, there still remain concerns over Daesh's alternative moneymaking methods like Zakat — a tax levied on Muslims for fighting holy wars — which is said to bring in hundreds of millions of dollars, almost the same amount as its other violent activities, reports Fox News.

Wealthy citizens and businesses are charged 2.5%, farmers have to contribute 5% of irrigated crops and 10% rain-fed crops while doctors contribute their services.